The successful operation of the host defense system is the result of several processes that work together to eliminate foreign pathogens. Coordinated innate and acquired immune responses are required, and many secreted and cell-associated factors have been identified as important mediators coordinating and regulating these two arms of host defense. Chemokines are a family of cytokines that act as chemoattractants to guide leukocyte migration. They are secreted by a wide variety of cells and can be functionally divided into two groups, hemostatic chemokines and inflammatory chemokines. Hemostatic chemokines are constituently produced in certain tissues and control cells of the immune system during processes of immune surveillance, such as directing lymphocytes to the lymph nodes to allow them to screen for invasion of pathogens. Inflammatory chemokines are released from cells in response to a pathological event (e.g., pro-inflammatory stimuli such as IL-1 or viruses). They function primarily as chemoattractants as part of the inflammatory response and serve to guide cells of both the innate and adaptive immune systems to the site of inflammation. The C—C chemokine receptor type 4 (CCR4), plays a role in the progression of a number of inflammation-related and other disorders. The identification of compounds that modulate CCR4 function is an ongoing challenge.